The long-term goal of this project is to understand the adaptive mechanisms underlying control of postural orientation and equilibrium in stance and gait in order to ameliorate balance and gait disorders. Loss of sensory information in patients with neurological deficits and in the elderly result in problems with gait and balance, and the investigators hypothesize that by manipulating somatosensory information from the support surface they can reveal how somatosensory and vestibular information interact in balance and gait and gain insight into compensation for sensory loss. Specific Aim I: How do bilateral vestibular loss patients use somatosensory information for postural orientation and equilibrium during gait? Recent studies have shown that stepping-in-place on a circular treadmill ("podokinetic stimulation") produces adaptations in locomotor trajectories in normal subjects. The investigators will use adaptation to podokinetic stimulation to reveal how subjects with bilateral vestibular loss use somatosensory information to control navigation trajectories and equilibrium during locomotion. They hypothesize that loss of vestibular information increases reliance on the somatosensory/motor system for spatial orientation and equilibrium. Specific Aim II: Can repeated exposures to podokinetic stimulation result in changes in postural orientation for gait in normal subjects and patients with unilateral vestibular loss? The Investigators hypothesize that repeated exposure to podokinetic stimulation results in enhanced and long-term retention of adaptation in normal subjects, and that podokinetic stimulation can be used to develop rehabilitation approaches for the curved locomotor trajectories and dysequilibrium observed in patients with unilateral vestibular loss. Specific Aim III: What is the effect of adapting to stance on inclined surfaces on postural orientation in healthy subjects and subjects with vestibular loss? The investigators will characterize the long-term effects of adaptation to stance on inclined surfaces in vestibular loss and control patients to reveal the contribution of the somatosensory-motor system to postural orientation. They hypothesize that patients with loss of vestibular (especially otolith) function will demonstrate larger changes in both postural orientation and perceived tilt than normal controls and that active motor control is necessary for adaptation to inclined surfaces. A better understanding of how the somatosensory/motor system, together with the vestibular system, contributes to locomotion and stance posture will allow them to better identify and rehabilitate deficits in balance and gait.